Apparatus for drying metal strips



July 9, 1963 N. TURNER 3,097,078

APPARATUS FOR DRYING METAL STRIPS Filed Sept. 11, 1959 INVENTOR:

Norman Turner A T TORNE Y6.

3,097,078 APPARATUS FOR DRYING METAL STRIPS Norman Turner, Runcorn, England, assignor to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain Filed Sept. 11, 1959, Ser. No. 839,360 Claims priority, application Great Britain Sept. 12, 1958 3 Claims. (Cl. 34-155) This invention relates to the drying of metal strip; in particular it provides an improved process and apparatus for drying metal strip which has been degreased in an organic solvent.

It is known to remove grease and other contamination from the surfaces of metal strip at various stages of manufacture and processing by passing the strip in continuous length through a vessel or vessels, known commercially as a degreasing plant, containing an organic solvent, commonly trichloroethylene or perchloroethylene, so that the strip is immersed in the liquid solvent or the vapour or in both the liquid and the vapour, whereby the grease and other contamination are washed away. The strip is wet with solvent as it leaves the degreasing zone and, in order to prevent the loss of expensive solvent and contamination of the atmosphere with solvent vapour, means have to be provided to dry the strip before it leaves the degreasing plant. When the metal strip is travelling at relatively low speeds, i.e. at speeds up to about 100 ft./min., drying may be carried out by conventional means, such as passing the strip through a short heated drying tunnel, and exhausting the evaporated solvent to a condensing arrangement and/or a charcoal scrubber, by means of a fan so that the solvent vapour does not escape through the strip inlet and exit ports.

From time to time it has been proposed to increase the speed of the metal strip through the degreasing plant, e.g. to 500 ft./min. or even 1,000 ft./min., in order to match other high-speed processes which precede or follow the solvent degreasing stage. When the strip is travelling at such high speeds the conventional methods of drying entail the provision of a much larger plant because the heated drying tunnel must extend far enough to ensure that the strip does not leave the plant before all the sol vent has evaporated from its surface. Such large plants are expensive and occupy a lot of floor space.

My invention provides a process whereby metal strip is dried after degreasing in an organic solvent and whereby the escape of solvent vapour into the atmosphere is prevented Without the considerable extension to the degreasing plant that is needed when conventional drying methods are used, even when the strip is travelling at a speed of 1,000 ft./min. Indeed my invention is applicable to even higher strip speeds than 1,000 ft./1nin. My invention also provides an apparatus of small dimensions in which my drying process is carried out and which can quite simply be attached to the degreasing plant.

We have found that drying of the strip can be achieved by passing it in continuous length through a short tunnel and directing air at or above atmospheric temperature and at superatrnospheric pressure, or steam at superatmospheric pressure, transversely over both surfaces of the strip from a jet or a group of jets suitably positioned at one or more points along the tunnel. We have found that when the air or steam so introduced is led out of the tunnel at a point or points substantially opposite to the point or points at which it is introduced, the strip is freed from its adhering solvent almost instantaneously and it emerges from the tunnel completely dry. The air or steam led out of the tunnel carries with it the entrained solvent and can be conducted to a conventional condensing arrangement, whereby liquid solvent ice is recovered, or to a conventional charcoal scrubber in which the solvent is collected for recovery. As a further feature of my invention we have found that with my apparatus, shortly to be described, there is caused an inflow of air at the ends of the tunnel so that escape of solvent vapour into the atmosphere is also prevented.

According to the present invention, therefore, a process for drying metal strip which is wet with organic solvent after passing in continuous length through a solvent degreasing plant and for preventing the escape of solvent vapour from the surfaces of the metal strip into the atmosphere comprises passing the metal strip in continuous length through a tunnel and directing air or steam at superatmospheric pressure transversely across both faces of the strip from a jet or a group of jets jositioned at one or more points along the tunnel and leading the air or steam so introduced out of the tunnel at a point or points substantially opposite to the point or points at which it is introduced, whereby the solvent is removed from the metal strip by entrainment in the injected air or steam and an inflow of air is created at the ends of the tunnel so that escape of solvent vapour from the ends of the tunnel is prevented.

The present invention also provides an apparatus for carrying out a process according to the preceding paragraph, comprising a tunnel through which metal strip can be passed in continuous length, said tunnel being of large enough diameter to take the width of the metal strip comfortably and having at intervals along its length one or more exit pipes, suitably of the same diameter as the tunnel, set perpendicular to its axis in the plane of the path taken by the metal strip, and having substantially opposite to each of said exit pipes one or more inlet jets through which air or steam at superatmospheric pressure can be admitted to pass transversely across both faces of the metal strip and to leave the tunnel through the said exit pipes.

We have found that as the drying operation is almost instantaneous a surprisingly short length of tunnel is needed and We have also found that an inflow of air at the ends of the tunnel is obtained without providing any special throat or venturi arrangement in the region of the air or steam jets. Furthermore we have found that with the apparatus of the invention it is not necessary for the drying tunnel to be heated. The apparatus of my invention is, therefore, of compact and simple design as will be seen by reference to the drawing (not to scale) in which FIG. 1 shows a plan view and FIG. 2 shows an end elevation.

The apparatus consists essentially of tubes A and B joined in the form of a T, and one or more jets C inserted in tube'A at a point opposite to the opening of tube B. Tube A is the tunnel through which the metal strip D passes, lying flat in the same plane as that of tubes A and B; the metal strip D is wet with the solvent as it enters tube A at E direct from the degreasing zone; it is dried as it passes jets C and is dry when it leaves tube A at F.

Air or steam is introduced to tube A through jets C, passes over both faces of the metal strip D and out through tube B, carrying with it the solvent from the surfaces of the metal strip and causing also an inflow of air at the ends E and F of tube A, which air also passes out through tube B. The gases and entrained solvent passing out through tube B can be led away to a conventional solvent recovery apparatus.

Jets C may consist of any number of jets arranged symmetrically around the edge of the metal strip D. The arrangement may consist of a single jet, e.g. the centre jet only of FIG. 2, directed at the edge of the metal strip D, or it may consist of two jets, e.g. the outer pair of FIG. 2, set at an angle to each other so that. they deliver the air or steam obliquely on to opposite faces of strip D. Another suitable arrangement consists of the three jets shown in FIG. 2, the centre jet being directed at the edge of the metal strip D and the other two jets being set at an angle on each side of the centre jet so that they are directed obliquely at opposite faces of the metal strip D. If more than three jets are installed it will be understood that they are similarly set at suitable angles to each other so as to deliver the air or steam on to both faces of the metal strip D.

My apparatus is not limited to one set of jets C with its corresponding tube B, but when the metal strip is travelling at very high speed, e.g. 1,000 ft./min. or more, and when the width of the strip is greater than about in. further sets of jets C with corresponding tubes B may be installed at intervals along tube A as necessary to ensure complete drying of the metal strip. This arrangement is illustrated in FIGURE 3.

The diameter of tubes A and B is not critical but tube -A should be of a size to accommodate the metal'strip comtortably, for instance tube A may be 2 in. diameter to accommodate strip of 1 in. width and it may be 6 in. diameter to accommodate strip of 4-5 in. width. Tube B is suitably of the same diameter as tube A. The length of tube A is also not critical; we have found, for example, a length of 3 ft. to be generally suitable when working with one set of jets installed in a tube of 2-6 in. diameter.

The size of the jets and the angles at which they are positioned relative to the metal strip depend on the width of the strip and its speed of travel and also on the pres sure of the air or steam injected. One suitable arrangement will be seen by reference to the following example which illustrates but does not limit my invention.

Example An apparatus of the type shown in the drawing was assembled, having tube A 2 in. diameter and 36 in. long, tube B 2 in. diameter, both these tubes lying in a horizontal plane, and jets C consisting of three jets, each of M; in. orifice. The jets were arranged round an arc of a circle of A in. radius in a vertical plane perpendicular to tube A, with the centre lines of adjacent jets at an angle of 45 to each other. Steel strip 1 in. wide was passed through a triohloroethylene degreasing plant in the conventional manner and the wet strip emerging from the plant was drawn centrally through tube A, the strip lying flat in the horizontal plane. The jets were positioned so that the centre jet was opposite to and A" away from the edge of the strip. With the strip moving at a rate of 600 ft./min. and with air at atmospheric temperature and 20 p.s.i.g. pressure supplied to the jets, the strip emerged from tube A quite dry and there was created sufi'icient inflow of air at the ends of tube A to prevent entirely the escape of trichloroethylene vapour into the atmosphere.

The pressure of the air supplied to my apparatus may he lower or very much higher than the 20 p.s.i.g. used in the example, but we prefer to work with a pressure high enough to obtain sulficient inflow of air at the ends of tube A to prevent the escape of solvent vapour into the atmosphere and yet not so high that an unnecessarily large volume of air passes with the entrained solvent vapour to the solvent recovery system. When air is supplied to the jets it may be at substantially atmospheric temperature or at any temperature above atmospheric which is convenient. When steam is supplied to the jets it must be at a sufificiently elevated temperature to achieve the desired pressure.

What I claim is:

1. Apparatus for drying strip material comprising:

means defining an open-ended tunnel through which the strip material may be passed; a single gas outlet pipe positioned perpendicular to the axis of said tunnel intermediate the ends thereof and in the plane of the path to be taken by the strip material; said outlet pipe having a transverse cross section about equal in area to that of said tunnel; and a group of at least two gas inlet jets substantially opposite to said gas outlet pipe and arranged symmetrically in an are around the edge of the path taken by the strip remote from the outlet pipe; the discharge area of said jets being smaller than said transverse crosssection whereby gas, admitted through said jets during operation of the apparatus passes transversely across both faces of the strip material, creates an inflow of air at the ends of the tunnel and leaves the tunnel through said outlet pipe.

2. Apparatus according to claim 1 in which the tunnel is provided with a plurality of outlet pipes and opposite to each of said outlet pipes a group of at least two inlet jets arranged symmetrically in an are around the edge of the path taken by the metal strip remote from the outlet pipes.

3. Apparatus according to the claim 1 in which the group of inlet jets comprises three jets, the centre lines of neighbouring jets being set at an angle of approximately 45 to each other.

References Cited in the file of this patent UNITED STATES PATENTS 485,694 Haskell Nov. 8, 1892 938,713 Schilling Nov. 2, 1909 1,294,035 Boland Feb. 11, 1919 1,629,511 Kramer et a1 May 24, 1927 1,766,595 Buck June 24, 1930 1,947,546 Reading Feb. 20, 1934 2,022,260 Viviani Nov. 26, 1935 2,451,854 Mehler Oct. 19, 1948 2,469,270 Liebel May 3, 1949 2,811,409 Clapp Oct. 29, 1957 2,838,420 Valente June 10, 1958 FOREIGN PATENTS 419,527 Great Britain Nov. 12, 1934 

1. APPARATUS FOR DRYING STRIP MATERIAL COMPRISING: MEANS DEFINING AN OPEN-ENDED TUNNEL THROUGH WHICH THE STRIP MATERIAL MAY BE PASSED; A SINGLE GAS OUTLET PIPE POSITOINED PERPENDICULAR TO THE AXIS OF SAID TUNNEL INTERMEDIATE THE ENDS THEREOF AND IN THE PLANE OF THE PATH TO BE TAKEN BY THE STRIP MATERIAL; SAID OUTLET PIPE HAVING A TRANSVERSE CROSS SECTION ABOUT EQUAL IN AREA TO THAT OF SAID TUNNEL, AND A GROUP OF AT LEAST TWO GAS INLET JETS SUBSTANTIALLY OPPOSITE TO SAID GAS OUTLET PIPE AND ARRANGED SYMMETRICALLY IN AN ARC AROUND THE EDGE OF THE PATH TAKEN BY THE STRIP REMOTE FROM THE OUTLET PIPE; THE DISCHARGE AREA OF SAID JETS BEING SMALLER THAN SAID TRANSVERSE CROSS SECTION WHEREBY GAS ADMITTED THROUGH SAID JETS DURING OPERATION OF THE APPARATUS PASSES TRANSVERSELY ACROSS BOTH FACES OF THE STRIP MATERIAL, CREATES AN INFLOW OF AIR AT THE ENDS OF THE TUNNEL AND LEAVES THE TUNNEL THROUGH SAID OUTLET PIPE. 